1. Field of the Invention
The present invention relates to a cap with valve, such as a fuel cap or a radiator cap for automobiles, which is installed to an aperture of a container such as a fuel tank or a radiator and adjusts pressure in the container by flowing fluid such as air out of the container or into the container from outside when the pressure in the container is positive or negative.
2. Description of the Prior Art
FIG. 1 shows structure of a cap with valve in the prior art, for example, a fule cap to be installed to a filler neck of an automobile.
A fuel cap (hereinafter referred to as "cap") 1 in FIG. 1 is installed to a filler neck 10 of a fuel tank. A cap body 2 has a flow path 2a for fluid such as air and a stepped portion 2b formed on inner circumference of the flow path 2a. An annular seal member 3 is disposed in the flow path 2a and provided with lip elements 3a, 3b projecting in the same direction at outer and inner peripheries respectively, and the outer lip element 3a only is adapted to abut on the stepped portion 2b of the cap body 2. A support plate 4 is also disposed in the flow path 2a and provided at the center with a fluid flowing hole 4a so that the whole rear surface of the seal member 3 is adhered and the seal member 3 is biased by a spring 7 and urged to the stepped portion 2b of the cap body 2. Further, a valve plate 5 is disposed in the flow path 2a and abuts on the inner lip element 3b of the seal member 3 so that inner circumference of the inner lip element 3b is biased closable by a spring 8. In the cap 1, when pressure in the fuel tank is positive, the valve plate 6, the seal member 3 and the support plate 4 are elevated against the biasing force of the spring 7, and since the outer lip element 3a of the seal member 3 and the stepped portion 2b of the cap body 2 are separated from each other, fluid such as air in the tank flows through the gap between the outer lip element 3a and the stepped portion 2b. On the contrary, when the pressure in the fuel tank is negative, the valve plate 5 is lowered against the biasing force of the spring 8, and since the inner lip element 3b of the seal member 3 and the valve plate 5 are separated from each other, fluid such as air flows in the tank through the gap between the inner lip element 3b and the valve plate 5.
In this constitution of the prior art, however, in order that fluid such as air flows into or out of the tank at low pressure of 0.03.about.0.15 Kg/Cm.sup.2 using the springs 7, 8 having low spring constant, the outer and inner lip elements 3a, 3b, the stepped portion 2b of the cap body 2, the valve plate 5, the rear surface of the seal member 3 and the support plate 4 must be high in surface precision (particularly undulation precision) and severe quality control is required for manufacturing the parts.
In order to fix the seal member 3 to the support plate 4 in the cap 1 of the prior art, means such as adhesion, welding of plating is utilized and therefore much process number is required to assemble the seal member 3 to the support plate 4 and the assembling cost becomes high.
Further in the cap 1 of the prior art, respective parts are assembled to the cap body 2 in sequence of the spring 8, the valve plate 5, the support plate 4 with the seal plate 3 fixed thereto, the spring 7, and the spring shoe plate 6. Since the outer and inner lip elements 3a, 3b of the seal member 3 are formed on the same plane in the conventional cap 1, when the valve plate 5 is assembled the valve plate 5 is positioned at upper side of the stepped portion 2b of the cap body 2 on account of the biasing force of the spring 8. When the support plate 4, the spring 7, the spring shoe plate 6 and the like are assembled later, the assembling may be effected in the state that outer circumference of the valve plate 5 remains to catch the stepped portion 2b of the cap body 2. This will cause the wrong assebling.